1. Field of the Invention
The present invention relates to a digital-to-analog converter, and more particularly to a digital-to-analog converter based on the adaptive delta modulation method or the delta modulation method.
2. Description of the Prior Art
Digital-to-analog (hereinafter abbreviated to "D/A") converters based on the delta modulation method and D/A converters based on the adaptive delta modulation (hereinafter abbreviated to "ADM") method are used, for example, in karaoke apparatus. In such applications, D/A converters are used to mix a plurality of audio signals into one.
Conventionally, D/A converters of this type have an input terminal for receiving a first audio signal, an input terminal for receiving a second audio signal, current converters for converting digital audio signals received via those input terminals individually into current signals bit by bit, and current-to-voltage converters for converting the obtained currents individually into voltages. The two signals are eventually added together by a voltage adder. In such D/A converters, both the current-to-voltage converter and the voltage adder include an operational amplifier, and the current-to-voltage converter includes a capacitor as well. In this way, according to the prior art, the D/A converters need to be provided with two current-to-voltage converters, and thus with two capacitors, and this has been preventing cost reduction of such D/A converters.